Starch, a branched glucose polymer (α4-glucose chains with α6 branches), is a natural material found in plants and animals where it functions as an energy store. The polymer consists of amylose (long chained and lowbranched) and amylopectin (highly branched and short chained).
Degradable starch microspheres (DSM) are formed of cross-linked starch chains. Degradable starch microspheres have been used for temporary vascular occlusion both with and without the co-administration of cytotoxic drugs (treatment of tumours and prevention of haemorrhages) for many years, but are also used for topical and intraoperative hemostasis.
The starch microspheres are degraded in vivo by plasma amylase into oligosaccharides, maltose and eventually to glucose that enter the normal metabolism.
Microparticles of starch or modified starch have been shown in prior art, for example in U.S. Pat. No. 6,060,461 and WO 2009/091549, i.a. for biocompatible hemostasis.
Furthermore U.S. Pat. No. 3,812,252 relates to hydrolysed starch and the use thereof for treating wounds, including chronic ones.
Wound healing is the intricate process in which the skin or another organ repairs itself after injury. The classic model of wound healing is divided into four sequential, yet overlapping, phases: (1) hemostatic, (2) inflammatory, (3) proliferative and (4) remodelling.
Hemostasis is the primary phase in wound healing, which causes the bleeding process to stop. Within minutes from injury to the skin or other organ, platelets (thrombocytes) are activated and aggregate at the injury site to form a fibrin clot.
When endothelial injury occurs, the endothelial cells cease to inhibit coagulation and begin to secrete coagulation factors that induce hemostasis after injury. Hemostasis has three major steps: 1) vasoconstriction, 2) temporary blockage by a platelet plug, and 3) blood coagulation by conversion of fibrinogen to fibrin and formation of a clot that seals the hole until tissues are repaired.
In the inflammatory phase, bacteria and debris are phagocytised and removed, and factors are released that cause the migration and division of cells involved in the proliferative phase.
In about 2-3 days fibroblasts begin to enter the wound site, marking the onset of the proliferative phase even before the inflammatory phase has ended. This phase is characterised by angiogenesis, collagen deposition, granulation tissue formation, epithelialisation, and wound contraction. In angiogenesis new blood vessels are formed, necessary for the supply of oxygen and nutrients to the wound site for supporting later wound healing stages. Simultaneously, fibroblasts begin accumulating in the wound site, their number peaking at 1 to 2 weeks post trauma. By the end of the first week, fibroblasts are the main cells in the wound.
In the first 2 or 3 days after injury, fibroblasts mainly proliferate and migrate, while later, they are the main cells that lay down the collagen matrix in the wound site. Initially fibroblasts use the fibrin scab formed in the inflammatory phase to migrate across, adhering to fibronectin. Fibroblasts then deposit ground substance into the wound bed, and later collagen, which they can adhere to for migration. Granulation tissue, growing from the base of the wound, begins to appear in the wound already during the inflammatory phase, and continues growing until the wound bed is covered. Granulation tissue consists of new blood vessels, fibroblasts, inflammatory cells, endothelial cells, myofibroblasts, and the components of a new, provisional extracellular matrix. Re-epithelialisation of the epidermis occurs when epithelial cells proliferate and “crawl” atop the wound bed, providing cover for the underlying newly formed tissue.
Cell culture is the process by which cells are grown under controlled conditions. The historical development and methods of cell culture are closely interrelated to those of tissue- and organ culture. Animal cell culture became a common laboratory technique in the mid-1900s, but the concept of maintaining live cell lines separated from their original tissue source was discovered in the 19th century. Tissue culture is the growth of tissues and/or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar. In this specification cell culture and tissue culture will be used synonymously.
Some cells naturally live in suspension, without being attached to a surface, such as cells that exist in the bloodstream. Those cells can be grown in suspension. However, most cells derived from solid tissues are anchor dependent, so called adherent cells. Adherent cells require a surface, such as tissue culture plastic or a microcarrier, to grow on. Microcarriers for growing adherent cells are available, for example dextran microspheres. When adherent cells are harvested or passaged (transport of subculture), the cells need to be detached from the surface it has grown on. Commonly this is done by the addition of a mixture of trypsin-EDTA to the culture.
Vascular embolisation (occlusion) is used as a minimally-invasive alternative to surgery. The purpose of embolisation is to prevent blood flow to an area of the body, creating ischemia, which effectively can shrink a tumour or block an aneurysm.
The procedure is carried out as an endovascular procedure, by a consultant radiologist in an interventional suite. It is common for most patients to have the treatment carried out with little or no sedation, although this depends largely on the organ to be embolised.
Access to the organ is gained by means of a guidewire and catheter(s). The artificial embolus used is usually one of the following methods: coil or hydrocoil, particles, foam or plug.
Agents used in embolisation therapy are i.a. liquid embolic agents which are able to flow through complex vascular structures. Examples of such are ethiodol, made from iodine and poppyseed oil which is a highly viscous agent and is usually used for chemoembolisations, especially for hepatomas; sclerosing agents, which will harden the endothelial lining of vessels and ethanol.
Particulate embolic agents, are also used to embolise precapillary arterioles or small arteries. Gelfoam® temporarily occludes vessels for 5 weeks. Microspheres are commonly used agents for both bland embolisation and chemoembolisation. Polyvinyl alcohol (PVA) and acrylic gelatin microspheres are not degradable in-vivo, hence they remain permanently in the patient. Depending on the situation, different sizes of microspheres are used, ranging from about 50 μm to about 1.2 mm in diameter.